1. Field of the Invention
The present invention, in general, relates to semiconductor device manufacturing methods and, in particular, to methods for the formation of refractory metal nucleation layers.
2. Description of the Related Art
Semiconductor devices (e.g., silicon integrated circuits) often include metal interconnect structures that serve a variety of purposes, including carrying electrical signals between individual device elements, the provision of power, supplying a connection to ground and furnishing a connection to external apparatus. Such interconnect structures include horizontal patterned metal layers separated by intermetal dielectric (IMD) layers formed of, for example, silicon dioxide (SiO2). The horizontal patterned metal layers are connected by vertical metal interconnects (referred to as vias) formed in the IMD layer.
One form of conventional via includes a titanium-nitride (TiN) barrier layer and a tungsten (W) core. The tungsten core is normally formed using a tungsten chemical vapor deposition (CVD) reaction. It is difficult to initiate the deposition of a high quality tungsten layer on a TiN barrier layer using tungsten hexafluoride (WF6) and hydrogen (H2) gases only, as this approach results in a long xe2x80x9cincubation time,xe2x80x9d i.e., the time between when the gases are introduced to a substrate (e.g., a silicon wafer) and when the deposition is initiated. This approach also results in a tungsten layer with poor thickness uniformity. These problems can be overcome using a CVD reaction that involves reduction of WF6 with monosilane (SiH4) to deposit a tungsten nucleation layer on the TiN barrier layer. Tungsten deposition by reduction of WF6 with SiH4 has little or no incubation time on a TiN barrier layer, and the resulting layer has minimal thickness nonuniformity. Tungsten is subsequently deposited on the tungsten nucleation layer using, for example, the aforementioned tungsten CVD reaction of WF6 and H2.
When tungsten layers are deposited by reduction of WF6 with SiH4, the reaction is typically conducted at a relatively low pressure (e.g., 40 Torr or less) to avoid gas phase nucleation and resultant particle formation. The tungsten deposition rate in this CVD process is determined, among other factors, by the pressure at which the reaction is carried out. By reacting at a relatively low pressure, a low deposition rate is achieved. Since the tungsten nucleation layer is deposited at a relatively low pressure and the tungsten core may be formed at a relatively high pressure (using, for example, the reduction of WF6 by H2), process time can be expended cycling and stabilizing between the two deposition pressures. This pressure cycling decreases the effective throughput of the process.
Still needed in the field, therefore, is a high throughput process for forming a refractory metal nucleation layer. In addition, the process should have a high effective throughput.
The present invention provides a process for forming a refractory metal nucleation layer (e.g., a tungsten nucleation layer) with both a high throughput and a high effective throughput. Processes according to the present invention employ a relatively high pressure (i.e., a pressure between 40 Torr and 300 Torr) during formation of the refractory metal nucleation layer. This relatively high pressure facilitates fast wafer temperature stabilization and fast reactions during formation of the refractory metal nucleation layer and, thus, a high throughput process. In addition, the inventive process can be combined with a conventional tungsten deposition technique (e.g., the hydrogen reduction of tungsten hexaflouride to form a tungsten core layer) conducted at a relatively high pressure without the need to expend process time cycling between two different pressures. The use of a relatively high pressure, therefore, enables a high effective throughput process since the pressure cycling required for a subsequent tungsten core layer deposition is eliminated.
An embodiment of a method for the formation of a refractory metal nucleation layer (e.g., a tungsten nucleation layer) on a semiconductor device substrate includes first depositing a metallic barrier layer (e.g., a titanium-nitride or tantalum-nitride barrier layer) on the semiconductor device substrate. Next, the metallic barrier layer is exposed to a silicon-containing gas (e.g., a silane gas such as monosilane [SiH4]) to form a layer of silicon (e.g., a monolayer of silicon) on the metallic barrier layer. The layer of silicon is then exposed to a refractory metal-containing gas (e.g., tungsten hexaflouride, WF6) such that the refractory metal-containing gas undergoes a reduction reaction with the layer of silicon. The result of this reduction reaction is the formation of a refractory metal layer (e.g., a tungsten metal layer) on the metallic barrier layer. If desired, the silicon-containing gas can be mixed with a nonreactive gas, such as helium or argon, to effectively mix and distribute the silicon-containing gas evenly across the semiconductor device substrate. Subsequently, an alternating exposure of the refractory metal layer to the silicon-containing gas and the refractory metal-containing gas is conducted. This alternating exposure serves to deposit additional refractory metal on the refractory metal layer and thus increase the thickness of the refractory metal layer and form a refractory metal nucleation layer.
By initially forming a layer of silicon on the metallic barrier layer, the uniformity, smoothness and homogeneity of the subsequently formed refractory metal nucleation layer is beneficially improved in comparison to refractory metal nucleation layers formed by conventional processes. Furthermore, by introducing the silicon-containing gas and the refractory metal-containing gas separately, the problem of gas phase nucleation and resultant particle formation at relatively high pressures is eliminated.
A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings.